A patent to Land, 1,955,923, concerns a light valve involving a dispersed mass of polarizing particles suspended in a light-transmitting medium, and applying to said particles an electrically controlled field of force, whereby the absorption of a light beam within the suspension may be altered. The polarizing bodies preferably employed are relatively small crystals. The crystals used should have some physical property which is susceptible to the field of force to be applied. When a magnetic field is employed the crystals turn or rotate in the suspension so their axes tend to orient similarly.
In accordance with Goldberg et al U.S. Pat. No. 3,927,930, finely divided ferrite particles, e.g. having a particle size of about 0.02 micron in diameter, are suspended in a light-transmitting inert medium, preferably water, on a transparent support. A magnetic field is applied to the ferrite suspension whereupon the ferrite particles orient themselves in the medium to form elongated, line-shaped agglomerates which polarize visible light passing through the magnetized suspension. The medium may, for example, comprise a polymerizable monomer which may be polymerized while in the magnetic field to freeze the ferrites in the oriented attitude in the solid polymeric medium. Photomicrographs were said to show regular line-shaped agglomerates of ferrite particles about 0.4 microns apart.
Ordering phenomena of particles, polystyrene spheres, in magnetic fluids have been studied, see A. T. Skjeltorp, J. Appl. Phys. 57 (1), pp. 3285-3290, 15 Apr. 1985, and Physical Review Letters, 51 (25), pp. 2306-2309, Dec. 19, 1983. Particle configurations in magnetic fluids have been described by R. W. Chantrell et al, J. Phys. D:Appl. Phys. 13 (1980) L119-2.
A 3M Light Control Film has been described in a brochure 98-0439-4252-7 (125) R1 XY, referencing Industrial Optics/3M, Building 223-4W, 3M Center, St. Paul, Minn. 55144-1000, 612/733-4403. The brochure illustrates a film with 0.030 inch (762 microns) thickness with light control louvers stated to be 0.0005 inch (12.6 microns) thick and 0.005 inches (126 microns) or 0.010 inches (252 microns) spacing. U.S. Pat. No. 4,082,433, assigned to Minnesota Mining and Manufacturing Company, states that internally louvered sheets can be made by skiving a continuous web from a cylindrical billet that has been prepared by compressing an assembly of alternate circular layers of clear polymeric material and black or other opaque or transparent colored layers. To improve the clarity of the product, clear films may be laminated or coated on each side of the skived web. U.S. Pat. No. Re. 27,617, assigned to Minnesota Mining and Manufacturing, further describes the manufacture of such film.
U.S. Pat. No. 3,707,416 has an object to produced louvered films having uniform angles of louvers from the vertical, and a process involving skiving from a skewed billet. U.S. Pat. Nos. 4,764,410 and 4,766,023 concern composite structures involving coating of louvered films, and cite a number of prior patents relating to louvered films and their applications. U.S. Pat. No. 4,772,096 concerns a light-shader intended to prevent reduction of contrast ratio of views in a display, generation of moires and devastion of images in the views. The light shader includes a light-shading film on a light-transmissive substrate plate. The light-shading film includes a plurality of opaque walls standing along its thickness and defining corresponding light-transmissive cells. Such opaque walls can be formed by opaquely dyeing a set photosensitive resin and transparent cells by eliminating and unset photosensitive resin by alkaline cleaner to form micro-openings. U.S. Pat. No. 4,772,097 concerns a light control sheet comprising transparent layers and reflection layers interposed between the walls of opaque louver elements. Preparation methods include slicing a material which has lamination layers and photoetching.